Increasing integration of devices enables smaller finished systems and products, and multiple devices are often packaged together to increase integration. For example, a high voltage or high current capable field effect transistor (FET) semiconductor device may be packaged with a gate driver circuit on a second semiconductor device. The gate driver supplies the gate voltage to operate the high voltage FET. Because the two devices may be fabricated in different semiconductor technologies, the two functions are provided on separate semiconductor devices. In an alternative example, an analog integrated circuit having active devices such as transistors may be packaged in a single module alongside a passive integrated circuit device that includes sensors, photocells, inductors, capacitors or resistors that are used in conjunction with the analog integrated circuit to form a complete circuit in a single packaged device. In still additional examples, a general purpose processor may be packaged with a specialized co-processor to enhance performance of a processing unit.
Packages that contain two or more semiconductor devices in a single package are referred to as “multichip modules.” To couple a multichip module to a system board, a surface mount multichip module package includes external terminals for mounting to the system board. In an example, a quad flat no-lead (QFN) package or dual flat no-lead (DFN) package is used which has terminals on at least one, and up to four, sides of a rectangular or square molded flat package. The no-lead terminals lie within the area of the body of the package. In an alternative, a “leaded” package has leads that extend away from the body of the package. The leads may be formed to have surfaces co-planar with the body of the package for use in surface mounting. In one example the semiconductor devices within a QFN package can be mounted “face up” (with the active surface oriented away from the leads of the package) and arranged on a substrate, such as a conductive lead frame, that has two or more device mounting areas. Wire bond or ribbon bond connections are made between bond pads on the semiconductor devices and leads of the lead frame for making connections. The lead frame includes conductive lead portions that form the external terminals of the finished multichip module package. Face up and wire bonded multichip module packages can require a large system board area, as the mounted semiconductor devices have to be spaced apart to allow room within the multichip module for the wire bond connections to be made to leads of the lead frame. Another approach uses “flip chip” or face down orientation of the semiconductor devices with respect to the substrate. In a flip chip package the semiconductor devices have conductive posts or pillars formed on the bond pads on the active surface of the semiconductor devices. The pillars extend from the active surface but lie within the surface area of the semiconductor device. The semiconductor devices are then turned face down, or “flipped”, so the active surface faces the mounting surfaces of substrate, for example a leadframe. The ends of the posts or pillars are bonded to the pads on the leadframe using solder and/or flux in a thermal reflow process. Because the electrical connections in a flip chip package are made beneath and within the area of the semiconductor devices, the board area for the flip chip multichip package that is needed on a system board is somewhat reduced (when compared to a wire bonded arrangement). However the connections needed between the two semiconductor devices in the multichip module require the use of leads or wire bonds that also increase the overall package area.